312 CONDITION OF THE FLOOR OF THE OCEAN. 



to extend the area with depths greater than 1,000 fathoms and to show 

 that numerous volcanic cones rise from the general level of the floor of 

 the ocean-basins up to various levels beneath the sea-surface. 



The areas marked out by the contour-lines of depth are now estimated 

 as follows: 



Between the shore and 100 fathoms, 7,000,000 square geographical miles, or 7 per 

 cent of the sea-bed. 



Between 100 and 1,000 fathoms, 10,000,000 square geographical miles, or 10 percent 

 of the sea-bed. 



Between 1,000 and 2,000 fathoms, 22,000,000 square geographical miles or 21 per cent 

 of the sea-bed. 



Between 2,000 and 3,000 fathoms, 57,000,000 square geographical miles, or 55 per cent 

 of the sea-bed. 



Over 3, 000 fathoms, 7,000,000 square geographical miles, or 7 per cent of the sea-bed. 



Total, 103,000,000 square geographical miles, 100 per cent. 



From these results it appears that considerably more than half of the 

 sea-floor lies at a depth exceeding 2,000 fathoms, or over two geo- 

 graphical miles. It is interesting to note that the area within the 100- 

 fathom line occupies 7,000,000 square geographical miles, whereas the 

 area occupied by the next succeeding 900 fathoms (viz, between 100 

 and 1,000 fathoms) occupies only 10,000,000 square geographical miles. 

 This points to a relatively rapid descent of the sea-floor along the con- 

 tinental slopes between 100 and 1,000 fathoms, and therefore confirms 

 the results gained by actual soundings in this region, many of which 

 indicate steep inclines or even perpendicular cliffs. Not only are the 

 continental slopes the seat of many deposit-slips and seismic disturb- 

 ances, but Mr. Benest has given good reasons for believing that under- 

 ground rivers sometimes enter the sea at depths beyond 100 fathoms, 

 and there bring about sudden changes in deep water. Again, the rela- 

 tively large area covered by the continental shelf between the shore 

 line and 100 fathoms points to the wearing away of the land by current 

 and wave action. 



On the Challenger charts all areas where the depth exceeds 3,000 

 fathoms have been called " deeps," and distinctive names have been con- 

 ferred upon them. Forty -three such depressions are now known, and 

 the positions of these are shown on the map here exhibited; 2-1 are 

 situated in the Pacific Ocean, 3 in the Indian Ocean, 15 in the Atlantic 

 Ocean, and 1 in the Southern and Antarctic oceans. The area occu- 

 pied by these 89 deeps is estimated at 7,152,000 square geographical 

 miles, or about 7 per cent of the total water surface of the globe. 

 Within these deeps over 250 soundings have been recorded, of which 

 24 exceed 4,000 fathoms, including 3 exceeding 5,000 fathoms. 



Depths exceeding 4,000 fathoms (or 4 geographical miles) have been 

 recorded within eight of the deeps, viz: In the North Atlantic within 

 the Nares Deep; in the Antarctic within the Ross Deep; in the Banda 

 Sea within the Weber Deep; in the North Pacific within the Chal- 



